Methods and systems for engine starting

Abstract

A system for improving engine starting is disclosed. In one example, an engine starting is improved by providing a predictable load to the engine during engine starting. The predictable load may be provided by controlling alternator field voltage during the engine start.

The invention claimed is: 
     
       1. A vehicle system, comprising:
 an engine that is selectively shut-down during engine idle-stop conditions; 
 a battery; 
 a starter; 
 a DC/DC converter electrically coupled to the battery, the DC/DC converter configured to provide a regulated voltage output; 
 an alternator including an alternator field coil excitation circuit, the alternator field coil excitation circuit electrically coupled to an output of the DC/DC converter during an engine start, the alternator mechanically coupled to the engine; and 
 a controller with computer readable instructions for,
 during an engine restart from idle-stop conditions, adjusting engine torque via at least one torque actuator. 
 
 
     
     
       2. The vehicle system of  claim 1 , wherein the starter is powered by the battery during the engine start. 
     
     
       3. The vehicle system of  claim 1 , wherein an armature of the alternator is in electrical communication with the battery, the battery supplying power to the DC/DC converter, and wherein the alternator field coil excitation circuit is electrically buffered from the battery via the DC/DC converter. 
     
     
       4. The vehicle system of  claim 1 , wherein an output voltage of the DC/DC converter is greater than a voltage of the battery during engine cranking. 
     
     
       5. The vehicle system of  claim 1 , further comprising a diode in a circuit that electrically couples the battery to the alternator field coil excitation circuit, a cathode of the diode oriented towards the alternator field coil excitation circuit, and an anode of the diode oriented towards the battery, the diode electrically buffering the alternator field coil excitation circuit from the battery by limiting current flow in a direction from the alternator field coil excitation circuit to the battery. 
     
     
       6. The vehicle system of  claim 5 , further comprising a switch coupled in parallel with the DC/DC converter, the controller including further instructions for,
 during the engine restart, opening the switch to electrically buffer the alternator field coil excitation circuit from the battery; and 
 following the engine restart, closing the switch to bypass a buffer circuit between the alternator field coil excitation circuit and the battery. 
 
     
     
       7. The vehicle system of  claim 1 , wherein the DC/DC converter is further electrically coupled to one or more auxiliary electrical loads including interior vehicle lighting. 
     
     
       8. The vehicle system of  claim 1 , further comprising a power steering system electrically coupled to the alternator, the controller including further instructions for controlling a current supplied to the power steering system by the alternator during the engine start. 
     
     
       9. A method of controlling a vehicle system including an engine that is selectively shut-down during engine idle-stop conditions, comprising:
 during an engine start,
 electrically buffering an alternator field coil excitation circuit of an alternator from a battery supplying power to a starter; and 
 maintaining an alternator field coil excitation circuit input voltage to control a load applied to the engine via an alternator rotor. 
 
 
     
     
       10. The method of  claim 9 , further comprising, bypassing the electrical buffering of the field coil excitation circuit of the alternator after a voltage at the battery is greater than a threshold voltage. 
     
     
       11. The method of  claim 10 , wherein maintaining the alternator field coil excitation circuit input voltage includes maintaining the alternator field coil excitation input voltage via a DC/DC converter. 
     
     
       12. The method of  claim 9 , wherein the electrical buffering is via a switch.